"Gypsy" is surely the greatest overture ever written, "Camelot" is the most memorable and any of the overtures for the classic Rodgers and Hart shows by Hans Spialek ("On Your Toes" "Babes in Arms" "Pal Joey") are wonderous but my vote is for one of the most pioneering, trendsetting overtures. In an age when EVERY show had a five minute overture, (which BTW was mainly to force the audiece into their seats from the lobby and street as if to say "hey, the show really is starting" and yes, people DID walk in during the overture) "Brigadoon" gets the job done - sets the mood, identifies the location and revs up the audience in a mere one page overture (I assume 96 to 128 bars). Then 48 brief bars of vocal voice-over and straight into the exposition scene. Amazing and daring for its time.
http://www.broadwayworld.com/board/readmessage.cfm?thread=972787#3631451
http://www.broadwayworld.com/board/readmessage.cfm?thread=963561#3533883
http://www.broadwayworld.com/board/readmessage.cfm?thread=955158#3440952
http://www.broadwayworld.com/board/readmessage.cfm?thread=954269#3427915
http://www.broadwayworld.com/board/readmessage.cfm?thread=955012#3441622
http://www.broadwayworld.com/board/readmessage.cfm?thread=954344#3428699